Mounting a folding pad eye

[Lars_L]

When I looked in Wichards catalogue, I find a folding pad eye that I think should be good both for fastening the jackstay on deck and for fastening the lifeline in the cockpit. It has a breaking strength of 27 kN.
In another place I did find that the safety hook on a lifeline has a breaking strength of 28 kN. I assume that the webbing have a comparable breaking load. A chain isn’t stronger than the weakest link.
The pad eye has three holesfor 6 mm countersunkscrews. In another catalog I did find that a stainless A4 screw class 80 have a breaking strenght of 16 kN. If the load on the pad eye comes little oblique, all load will end up on one screw, and that will it not hold for.
I can have a screw of class 12.9 with a breaking strength of 24 kN, but they are not stainless. If I go up one size of the pad eye, it has instead three 8 mm screws, and one such has a strength of 29 kN.
How do you think I should get a pad eye that holds? Or am I thinking wrong about the load?
I am aware that the place I put the pad eye should be strong enough, but if not, it’s quite easy to fix.

[thinwater]

Originally Posted by Lars_L

When I looked in Wichards catalogue, I find a folding pad eye that I think should be good both for fastening the jackstay on deck and for fastening the lifeline in the cockpit. It has a breaking strength of 27 kN.
In another place I did find that the safety hook on a lifeline has a breaking strength of 28 kN. I assume that the webbing have a comparable breaking load. A chain isn’t stronger than the weakest link.
The pad eye has three holesfor 6 mm countersunkscrews. In another catalog I did find that a stainless A4 screw class 80 have a breaking strenght of 16 kN. If the load on the pad eye comes little oblique, all load will end up on one screw, and that will it not hold for.
I can have a screw of class 12.9 with a breaking strength of 24 kN, but they are not stainless. If I go up one size of the pad eye, it has instead three 8 mm screws, and one such has a strength of 29 kN.
How do you think I should get a pad eye that holds? Or am I thinking wrong about the load?
I am aware that the place I put the pad eye should be strong enough, but if not, it’s quite easy to fix.

As a jackline anchor, the load will be virtually in shear, without enough vertical component to fuss over. Personally, an have no interest in folding pad eyes for this as there is a chafe issue (against non-skid) and jackline should be rigged most of the time.

As a cockpit anchor, I would be FAR more concerned about a tether that will limit impact force; if you pass 1200 pounds you will have broken ribs.

Try these: very well proven. Thousands of climbers have fallen against them, purpose-built, made for clipping biners. Many brands.


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[Lars_L]

I can imagine that it can bear the load when attached with a 12 mm bolt. But it is not any comfortable to sit on.

Wichard said that their lifeline comply with EN 1695 / ISO 12401 norm and (although I have not read it) it requires a breaking strenght of more than 20 kN. And it must also apply to the fixing point in the cockpit. I agree that the ribs do not pass a chock load of 20 kN, but that is why there is elastic lifelines.

[rognvald]

Lars,
You mentioned a "jackstay." Do you mean "jackline?"

[thinwater]

Originally Posted by Lars_L

I can imagine that it can bear the load when attached with a 12 mm bolt. But it is not any comfortable to sit on.

Wichard said that their lifeline comply with EN 1695 / ISO 12401 norm and (although I have not read it) it requires a breaking strenght of more than 20 kN. And it must also apply to the fixing point in the cockpit. I agree that the ribs do not pass a chock load of 20 kN, but that is why there is elastic lifelines.

I don't know what you mean by lifelines in this sentence. Lifelines go around the boat, are SS or dyneema, and are not the topic. Local differences in English usage, I am sure.

Jacklines can be either somewhat elastic (polyester) or SS; polyester will absorb some shock, and there have been no harness/tether failures associated with sailors clipped to jacklines for that reason. However, if you clip direct to the padeye (common in the cockpit) there is no jackline, the shock load can reach 20kn, and there have been failures. Fly across the cockpit and the force is no less than a climber fall factor 1 (speed is the same). There is no max force requirement in the EN drop test standard. Check my math.

Sail Delmarva: Sample Calculations for Jackline Stress and Energy Absorption

But there is a much simple test. Put on your harness, clip the tether to something rigid, allow about 6 feet of slack in a polyester tether line, as though you were at the other side of cockpit, and run as fast as you can, as though you were hit by a big wave during a knockdown. Actually, please do not do this, as you will sustain serious rib injury. Try it slow first. Write back and tell us about your experience.

In my experience (I have tried this) you will get hurt, and thus I use dynamic line for tethers. Safer and more comfortable.

[Lars_L]

rognvald
Yes, I mean jacklines.

thinwater
Yes, I believe in you without hurting myself. But is not a Dynema line very dumbly as teather line? Is it not better if it had, like the jacklines, been made of some more elastic material like polyester or even more elastic polypropylene?

BUT my real problem is, do the fastening of my pad eye holds for the load?

[Lars_L]

Now I have talked with person how knows a lot abut mechanic. He say:

When the screws are tighten to the right moment according the tables (i.e. 9.76 Nm for a 6 mm screw with oil, class 70) it will be preloaded with a force of 2/3 of the stretching load. To achieve this the base where the pad eye are mounted has to be rigid. If it’s done this way, all screws will take the load even if its oblique. So if one screw with the breaking strength of 14 kN will break, the three together gives a strength of 42 kN, and that’s enough. But if don’t tighten them enough, it will be only one screw that takes the load, and break.

I shall say that I believe him. He gave me a couple of example from the real life, but I’m not so sure that I can argue for it.

[thinwater]

Originally Posted by Lars_L

rognvald
Yes, I mean jacklines.

thinwater
Yes, I believe in you without hurting myself. But is not a Dynema line very dumbly as teather line? Is it not better if it had, like the jacklines, been made of some more elastic material like polyester or even more elastic polypropylene?

BUT my real problem is, do the fastening of my pad eye holds for the load?

Polyester is not very elastic either. That is why most yacht line is polyester. In fact, that is what I suggested trying. It will hurt. A lot.

As for the mounting, You will not have all of the load on one screw in any scenario; if the load is horizontal, they share, if vertical they share, if oblique, the base is wider than the pad eye is tall and leverage helps. Try a force diagram.

The MAIN point is to avoid the force. If you take 20kn on a chest loop you'll be dead anyway. The car manufacturers and military have studied this, and any force much over 5 kn on a single strap will break bones.

Most polypropylene rope is crap. I don't know what you mean about that.

[Lars_L]

If the teather is made of an elastic rope, the chock load will be much smaller. If I have attached the teather to an anchor point in the cockpit there will not be anything that reduce the chock load except the elastic in the teather line. Polypropylene are known to be elastic, but it’s also known to be a crap.